The invention relates to an improved dryer oven for a textile web and other sheet-like material which is constructed for higher efficiency and cleanability.
In the textile industry, it is common to dry a traveling textile web by passing it through a dryer oven on tenter chains. Other industries also use ovens for drying sheet-like material which travels through the oven. Normally, the ovens are quite large and require that an attendant enter the oven in order for it to be cleaned of waste, dust, and other contaminant particulate matter. In the case of drying fabrics containing volatiles, the residual condensed vapors must often be cleaned from the oven parts, burners, etc. The interior of the typical dryer oven has been constructed as a large box, for example, see U.S. Pat. Nos. 4,295,284. An average housing for a textile tenter oven is 90 feet in length, 15 feet in width, and 7 feet in height. The oven also includes up to three penthouses on top which house burners, etc., each penthouse is about 10 feet in length, 15 feet in width, and 8 feet in height. The oven housing is not compact and the attendant must enter the large and dark housing in order to clean the parts. The large size and thermal mass in oven structure normally do not allow for the oven to cool down in time for cleaning. Because of the nature of the cleaning operation and the necessity of entering the large housing box, the oven is not cleaned or the attendant often does not perform a thorough job because the oven is still hot or warm, reducing the efficiency and life of the oven. If volatile ovens are not cleaned properly, they can quite easily catch on fire resulting in damage and danger. Explosions quite often result in oven damage. The drying efficiency of the prior art heater ovens is a problem to which little attention has been given. Attention has been somewhat diverted from the problems of cleanability and efficiency and drawn instead to the other mechanical aspects associated with conveying the fabric through the large housing box while contacting opposing sides of the web or sheet material with hot air.
Typically, the textile web drying ovens have consisted of one large housing in which two superposed dryer units are arranged between which the web travels. A plurality of spaced hot air ducts normally are used across the dryer units transverse to the direction of web travel as shown in U.S. Pat. No. 3,739,491. Once the hot air leaves the ducts, it impinges upon the top and bottom of the web. Air control in this area is crucial to the dryer efficiency and performance. Uniform drying of each side of the web is critical. If drying is uneven, streaking or shading of dyed fabrics may result through wicking of the dye. In the case of coated fabrics like latex coated furniture fabrics, the coating will overcure in some areas while undercure in other areas when the drying rate is not uniform. After the fabric is converted to furniture, fabric shading occurs in the areas of overcuring resulting in customer complaints and returned furniture. In other applications, it may be desirable to subject opposite sides of a web to different drying temperatures.
Due to the fact that there are many different types of fabric which now need to be dried on the same dryer, many dryers are being made with variable speed blowers to accommodate the different fabrics on the same dryer. However, the existing single nozzle type of air distribution system is still being used in combination with the variable speed blower. The result is the development of eddy currents at certain speeds which result in unbalanced air distribution and uneven drying.
Various structures and methods are used to impinge the hot air upon the traveling web. The single nozzle distribution system is typical of that shown in U.S. Pat. Nos. 4,516,332 and 4,523,391. U.S. Pat. No. 2,144,919 discloses an arrangement of a web drying oven wherein hot air is distributed between transverse ducts, rather than through the ducts as in Pat. No. 3,739,491. In the '919 patent, the ducts return the air after contacting the traveling web. The ducts are contoured to provide special air flow treatment of the air passing between the ducts to contact the web. In particular, the ducts are shaped to define nozzles which deliver the jets of hot air against the web at angles from 20-30 degrees. U.S. Pat. No. 3,678,599 discloses particular arrangements of air ducts with a perforated concave rib between adjacent ducts. This arrangement is said to stabilize the web moving longitudinally. In this arrangement, the transverse ducts are used for the return of air rather than distribution of hot air. Slot shaped openings are defined at the ends of the rib which direct the hot air in opposite directions. The ducts are said to consist of airfoil sections. The selection of the cross-section of the perforations in the ducts and the vacuum inside the ducts is said to control desired flow conditions. However, this results in a relatively theoretical and complicated determination of air flow characteristics which may not be susceptible of exact determination or practical embodiment. There is also a space between adjacent pairs of ducts in which there is no flow treatment. U.S. Pat. No. 3,060,594 discloses an apparatus for drying webs with hot air or other medium in which provision of a desired air flow pattern is sought to accomplish contact-free and tension-free guiding and drying of webs freely floating within a treatment chamber. In this case, air is discharged from transversely extending ducts and is returned between the ducts.
Various arrangements have been provided for forcing the hot air into the dryer sections. Dual blowers are shown in U.S. Pat. No. 4,137,649 and a single blower is shown in U.S. Pat. No. 4,516,332. Typically, these blowers deliver the air through trapezoidal shaped boxes as illustrated in the aforesaid patents. The air may be heated by a burner or conventional means and taken in by the intake side of the blower. The hot air taken in may also be mixed with the return air from the dryer sections as illustrated in the '332 patent. A single source of heat may be used such as in U.S. Pat. No. 4,551,928, or plural sources of heat may be used such as shown in the '649 patent, one each for the two blowers.
Accordingly, an important object of the invention is to provide a compact dryer oven for a web and the like material which provides balanced hot air distribution for even drying of the web.
Another object of the invention is to provide a compact dryer oven for a web and the like material having superposed oven housing which may be operated at different temperatures to subject opposite sides of the web to different drying conditions.
Another object of the invention is to provide a compact dryer oven for a web and the like material having superposed oven housing with air flow characteristics which facilitate travel of the web between the housings and through the oven while floated by air.
Another object of the invention is to provide a web drying oven which is compact and easily cleanable.
Another object is to provide a compact web drying oven having a minimum interior volume so that accumulations of volatile vapors is reduced and a releasable upper housing that will open should an explosion occur to reduce dryer damage.
Another object of the present invention is to provide a dryer oven for a web and like sheet material which is compact and has an upper pivotal housing which may be opened for access to clean the oven without the need of entering the dryer box.
Another object of the invention is to provide a dryer oven for a web and the like material having improved hot air flow distribution for more efficient drying and support of the web traveling through the treatment section of the oven.
Another object of the invention is to provide a dryer oven for a web and the like material which is compact and has a closed circuit air distribution system with a short path which eliminates the use of long supply ducts and increases the number of air changes per minute to provide more efficient and protective use of blower horsepower and a lower temperature differential between supply air and return air, all of which enhances the efficiency of the oven.
Another object of the invention is to provide a dryer oven for a web and the like material having a hot air distribution system which uses a plurality of separate nozzle orifices which balance the air distribution and provide a combination tangential and center lift air flow relative to the traveling web which accelerates drying rates without using high air forces that would tend to push down the pile of pile fabrics and push in the chemical compounds of coated fabrics.
Another object of the invention is to provide a compact dryer oven for a web and the like material in which the interior space and material used within the interior of the oven are both reduced which allows reduced heat mass inside the oven to provide for extremely fast start-up times and low energy consumption.